1. Field of the Invention
The present invention relates to an endoscope system, a processor device for an endoscope system, an operation method for an endoscope system, and an operation method for a processor device for calculating biological function information regarding the oxygen saturation of blood hemoglobin from an image signal obtained by imaging an observation target in a subject.
2. Description of the Related Art
In the medical field, it is common to perform diagnosis using an endoscope system including a light source device, an endoscope, and a processor device. In recent years, diagnosis of a lesion using the oxygen saturation of blood hemoglobin in biological function information has been performed. As a method of acquiring the oxygen saturation, a method is known in which first signal light and second signal light having different waveguide bands and different light absorption coefficients for oxygenated hemoglobin and reduced hemoglobin are alternately emitted to blood vessels in the mucous membrane and reflected light beams of the first and second signal light beams are detected by a sensor located at the distal end of the endoscope (refer to JP2012-100800A, JP2012-130429A, and JP2013-099464A). The ratio between signal values (hereinafter, referred to as a signal ratio) of pixels of an image signal corresponding to the reflected light of the first signal light detected by the sensor and an image signal corresponding to the reflected light of the second signal light detected by the sensor is maintained as a fixed value if there is no change in the oxygen saturation in the blood vessel. However, if there is a change in the oxygen saturation, the signal ratio is also changed accordingly. Therefore, it is possible to calculate the oxygen saturation based on the signal ratio of the image signals.